chapter 14 acids and bases. lemons contain citric acid, citric acid produces h + ions in your mouth...
TRANSCRIPT
Chapter 14
Acids and Bases
Lemons contain citric acid,
• Citric acid produces H+ ions in your mouth
• H+ ions react with protein molecules on your tongue
• The protein molecule changes shape – sending an electrical signal to your brain “Sour!”
Acids
• How do I identify an acid?
– HCl, H2SO4, HNO3
– First atom is hydrogen– Produces H+ ions in water
• HCl(aq) H+(aq) + Cl-(aq)
– HCl + H2O H3O+(aq) + Cl-(aq)
• H2SO4(aq)
• HNO3(aq)
Acids and Bases
• ACIDS• Taste sour• Dissolve many metals• Turn litmus paper red
• BASES• Taste bitter• Feel slippery• Turn litmus paper blue
Sodium hydroxide or “lye”
Carbonic acid, phosphoric acid
Citric acid
Tartaric acid
Sodium borate
Sodium carbonate “washing soda”
Arrhenius Theory
• Acids ionize in water to H+ ions and anions– HCl(aq)
• Bases ionize in water to OH- ions and cations– NaOH(aq)
• Neutralization reaction net ionic equation:–
Brønsted-Lowery Theory
• Acid is H+ donor– HCl(aq) H+(aq) + Cl-(aq)
• Base is H+ acceptor– NH3(aq) + H+(aq) ↔ NH4
+(aq)– H2O(l) + H+(aq) ↔ H3O+(aq)
• What else do NH3 and H2O has in common?–
• In the reaction, a H+ from the acid molecule is transferred to the base molecule
Conjugate Acids and Bases
• NH3(aq) + H2O(l) ↔ NH4+(aq) + OH-(aq)
• H2SO4(aq) + H2O(l) HSO4-(aq) + H3O+(aq)
• C5H5N(aq) + H2O(l) ↔ C5H5NH+(aq) + OH-(aq)
Base
Conjugate Base
Conjugate Acid
Acid
Strong versus Weak Acids
• Strong acids completely dissociate into ions– Major species: ions– Minor species: un-ionized acid
• Weak acids slightly dissociate into ions.– Major species: un-ionized acid– Minor species: ions
Strong versus Weak Acids
Strong versus Weak Acids
• Which solution contains the strong acid?
Strong versus Weak Acids
Strong Acids Weak Acids
HX(aq) H+(aq) + X-(aq) HX(aq) H+(aq) + X-(aq)
Nitric acid (HNO3)Most organic acids (acetic, oxalic, citric, fatty acids)
Sulfuric acid (H2SO4) Hydrofluoric acid (HF)
Hydrochloric acid (HCl)Carbonic acid - soda pop (H2CO3)
Hydrobromic acid (HBr)Hydroiodic acid (HI)
Phosphoric acid - in Coke (H3PO4)
Which Hydrogen atoms are acidic?
Strong versus Weak Bases• Strong bases completely dissociate into ions
– Major species: ions– Minor species: un-ionized acid– NaOH(aq) Na+(aq) + OH-(aq)
• Weak bases slightly dissociate, producing hydroxide ions.– Major species: un-ionized acid– Minor species: ions
– NH3(aq) + H2O(aq) ↔ NH4+(aq) +OH-(aq)
Strong versus Weak Bases
Strong Bases Weak Bases
MOH(aq) M+(aq) + OH-(aq)B(aq) + H2O(l) BH+(aq) + OH-
(aq)
Sodium hydroxide (NaOH) Ammonia, NH3
Potassium hydroxide (KOH) Lithium hydroxide (LiOH)
Bicarbonate, HCO3-
Calcium hydroxide (Ca(OH)2)
Strontium hydroxide (Sr(OH)2)
Amines (Carbon group-NH2)
Barium hydroxide (Ba(OH)2) Water (H2O)
Relative Strength of Conjugate Acids and Bases
• H2SO4(aq) + H2O(l) HSO4-(aq) + H3O+(aq)
• A strong acid has a weak conjugate base• A strong base has a weak conjugate acid
• A weak base has a strong conjugate acid• A weak acid has a strong conjugate base
Base
Conjugate Base
Conjugate Acid
Acid
Recognizing Acids and Bases
• Bases need a lone pair of electrons to accept a proton• Acids leave behind stable anions
Reactions of Acids and Bases
• Neutralization Reactions
• H2SO4(aq) + Ca(OH)2(aq) →
• Single Replacement Redox
• 3 H2SO4(aq) + 2 Al(s) →
• Acids react with metal oxides…
• 3 H2SO4 + Al2O3 →
Water
• NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
• H2SO4(aq) + H2O(l) HSO4-(aq) + H3O+(aq)
• Can act as an acid or base - amphoteric
Water
• Auto-ionization
• H2O(l) + H2O(l) ↔ H3O+(aq) + OH-(aq)
• At equilibrium, the [H3O+] and [OH-] are constant and equal.
– KW = [H3O+][OH-]=1x10-14 at 25°C
• What is the concentration of [H3O+] at equilibrium?
Acidic versus Basic Solutions• Every aqueous solution
contains water molecules, hydronium ions (H30+ or H+) and hydroxide ions (OH-)
• A neutral solution: – [H+] ~ [OH-]
• An acidic solution: – [H+] > [OH-]
• A basic solution: – [OH-] > [H+]
H+ OH-H2OH2O
H2OH2O
H+ OH-H2OH2O
H2OH2O
H+ OH-H2OH2O
H2OH2OH+
H+
OH-
OH-
pH scale
• Neutral: pH ~ 7• Acidic: pH < 7• Basic: pH > 7
• pH = - log [H3O+]
• Significant figures:
• [H3O+] = 1.0 x 10-3
• pH = 3.00
Measuring pH
4
1 2 3
5 6 7 8
9 10 11 12
4
pH meterUniversal Indicators
pH and pOH
• pOH = - log [OH-]
• KW = [H3O+][OH-] = 1 x 10-14
• pH + pOH = 14
• Calculate the pH of a solution with:
– [H3O+] = 1.0 x 10-8 M
– pOH = 8.00– [OH-] = 1.0 x 10-8 M
• Calculate the [H3O+] of a solution with:
– pH = 4.00– pOH = 6.00– [OH-] = 1.0 x 10-4 M
• Calculate the pH of 0.10 M HNO3 solution.
pH and pOH• pOH = - log [OH-]
• KW = [H3O+][OH-] = 1 x 10-14
• pH + pOH = 14
• Calculate the pH of a solution with:– [H3O+] = 9.5 x 10-9 M– pOH = 4.80– [OH-] = 1.3 x 10-2 M
• Calculate the [H3O+] of a solution with:– pH = 4.80– pOH = 5.67– [OH-] = 7.2 x 10-11 M
• Calculate the pH of 0.10 M H2SO4 solution.
• Calculate the pH of 0.10 M Ba(OH)2 solution.
Titrations
• To a colorless acidic solution, we will add base.• When the solution is basic, it will be red.• We are looking for the equivalence point where the
moles of H+ = moles of OH-
• We will determination of molarity of NaOH solution
Oxalic acidsolution
Add NaOH
(with indicator)
Basicsolution
Calculations
H2C2O4 + NaOH H2O + Na2C2O4
Mass ofH2C2O4 (g)
MolesH2C2O4
Moles NaOH
Concentration of NaOH solution (M)
Volume ofAdded NaOH
0.628 g 24.7 mL ? M
Buffers resist changes in pH
• Buffers contain large amount of an weak acid and its conjugate base
• HCl(aq) + NaC2H3O2(aq) • NaOH(aq) + HC2H3O2(aq) • Which of the following would constitute a buffer solution? (a) H2SO4 & H2SO3(aq) (b) HF(aq) & NaF(aq) (c) HCl & NaCl (d) NaCl & NaOH